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The Big One
The "Big One" is a hypothetical devastating that is predicted to occur in similar to or worse than the . San Andreas Fault The San Andreas Fault is a continental that extends roughly through . It forms the boundary between the and the *Its motion is (horizontal). *The slip rate along the fault ranges from 20-35 mm/yr. The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. Northern The northern segment of the fault runs from , through the , epicenter of the , then up the then offshore at near . *This is the approximate location of the epicenter of the . Central The central segment of the San Andreas Fault runs in a northwestern direction from Parkfield to . While the southern section of the fault and the parts through Parkfield experience earthquakes, the rest of the central section of the fault exhibits a phenomenon called , where the fault slips continuously without causing earthquakes. Southern The southern segment, which stretches from in all the way to the , is capable of an 8.1-magnitude earthquake. At its closest, this fault passes about to the northeast of Los Angeles. Such a large earthquake on this southern segment would kill thousands of people in Los Angeles, San Bernardino, Riverside, and surrounding areas, and cause hundreds of billions of dollars in damage. The Big One The risk is currently concentrated on the southern section of the fault, i.e. the region around Los Angeles, because massive earthquakes have occurred relatively recently on the central ( ) and northern ( ) segments of the fault, while the southern section has not seen any similar rupture for at least 300 years. *A massive earthquake on that southern section of the San Andreas fault would result in major damage to the - metropolitan area and other cities in , and counties in California, and in . *It would be strongly felt (and potentially cause significant damage) throughout much of , including densely populated areas of , , , , and , , in and , . *Older buildings would be especially prone to damage or collapse, as would buildings built on unconsolidated gravel or in coastal areas where water tables are high (and thus subject to ). The most recent forecast, known as (Uniform California Earthquake Rupture Forecast 3), released in November 2013, estimated that there is a 7% probability that an earthquake of magnitude 8.0 or greater will occur in the next 30 years somewhere along the San Andreas Fault. A different USGS study in 2008 tried to assess the physical, social and economic consequences of a major earthquake in southern California. That study predicted that a magnitude 7.8 earthquake along the southern San Andreas Fault could cause about 1,800 deaths and $213 billion in damage. Cascadia connection A 2008 paper, studying past earthquakes along the Pacific coastal zone, found a correlation in time between seismic events on the northern San Andreas Fault and the southern part of the (which stretches from to northern California). Scientists believe quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas within the past 3,000 years. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. *However the 1906 San Francisco earthquake seems to have been the exception to this correlation because the plate movement was moved mostly from south to north and it was not preceded by a major quake in the Cascadia zone. Earthquakes The San Andreas Fault has had some notable earthquakes in historic times: * : About were ruptured in central and southern California. Though it is known as the earthquake, the epicenter is thought to have been located far to the north, just south of . Two deaths were reported. Its was 7.9. * : About were ruptured in Northern California. The epicenter was near . At least 3,000 people died in the earthquake and subsequent fires. The magnitude was estimated to be 7.8. * : A magnitude 5.7 quake with an epicenter on the San Andreas fault in the ocean west of San Francisco and Daly City. * : About were ruptured (although the rupture did not reach the surface) near , causing 63 deaths and moderate damage in certain vulnerable locations in the San Francisco Bay Area. was about 6.9. This quake occurred on October 17, 1989, at approximately 5:04 pm PDT. * : On September 28, 2004, at 10:15 am PDT, a magnitude 6.0 earthquake struck the Parkfield area. It was felt across the state, including the San Francisco Bay Area. References Category:Safety